1. Technical Field
The present disclosure relates to an off-axial three-mirror optical system with freeform surfaces, and particularly to an off-axial three-mirror optical system with freeform surfaces which can achieve small F-number and large field angles.
2. Description of Related Art
Compared with conventional rotationally symmetric surfaces, freeform surfaces have asymmetric surfaces and more degrees of design freedom, which can reduce the aberrations and simplify the structure of the reflective scanning system. Thus, freeform surfaces are often used in off-axial three-mirror optical system.
However, conventional off-axial three-mirror optical systems with freeform surfaces are mainly applied to linear field of view with small field angles and large F-number, but the applications in the field of view with large field angles and small F-number are limited.
Another problem in some related art is the assembling and aligning of the conventional off-axial three-mirror optical systems with freeform surfaces is complicated, for the primary mirror, the secondary mirror, and the tertiary mirror in the conventional off-axial three-mirror optical systems with freeform surfaces are all separate from each other.
What is needed, therefore, is to provide an off-axial three-mirror optical system with freeform surfaces, which can achieve large field angles, small F-number and simple assembling and aligning.